Ive read somewhere that class 6 will be ok, but cant find any other info to find out which class i need?
i dont want to fork the money out for a 8gb sdhc Class 6 if the camera can only buffer at class 4.

The class rating is a load of BS imho.
I have class 4 cards that outperform class 6 cards, so you can't trust the rating.
Also, I've found that some cards don't work well in cameras for whatever reason, despite working well on the PC when tested at read/write speeds of close to 20MB/s, yet in my 500D I can't record more than a few seconds of video and then the camera stops.
Toshiba makes good cards imho and I'm using a SanDisk 20MB/s "HD Video" card now as I got a good deal on one. It's only a class 6 card, yet it perform better than the class 10 spec. However, it doesn't meet the 20MB/s rating on the card, although I guess 19MB/s isn't too bad.